Interaction among krill, whales and other animals in the Antarctic ecosystem

A trial was made to establish a model dealing with the interaction among krill and other predators in order to estimate the valid exploitation level not to impair the stock of krill and whale, based upon the dynamics of prey and predotor. As the present knowledge of the basic biological parameters for the dynamics is still poor, the present report mainly aimes to set up the model and find out what parameters are important rather than to obtain the result itself. At first the simple model with only one type of predator was used and the model was elaborated so as to include multiple predotors, and also to deal with the environmental influence. Equilibrium state, in which the MSY level of exploitation rate can be expected, can be attained almost 100 years later if we start from the present level of stocks of both krill and whales. According to the tentative calculation it was suggested that the influence of catch of krill upon the stocks of both krill and whales is very low even if 10% of the krill stocks is to be exploited for the period of 20 years or more. But the effect upon the stock of seal seems more significant than that upon whales when feeding competition is taken into consideration. Sensitivity of each parameter upon the long term estimation of the krill stock was tested. The most sensitive parameters are the reproduction rate of krill, and the carrying capacity of krill in the Antarctic. The type of feeding competition should be studied